Although most new shooters begin with factory ammunition, there are multiple advantages that encourage many to pursue “reloading.” Reloading is the reprocessing or recycling of previously fired cartridge cases into loaded ammunition. The advantages of reloading include reducing the cost of ammunition, being able to custom tune ammunition, enabling a firearm to be more versatile through use of a broader assortment of bullet styles, and enabling owners of obsolete firearms to continue to shoot even when factory ammunition is no longer available. Other advantages include affordability, and the ability to manufacture unusually precise ammunition for enhanced accuracy.
Modern rifle and handgun cartridges consist of the cartridge case, the primer, the propellant, and the bullet. The most costly and critical component of a cartridge is the case. In addition to holding all of the other components, the case provides a precision seal to ensure the high-pressure expanding gases remain in the firearm, and away from the shooter, to efficiently push the bullet out of the barrel. The brass case is the costliest component of the cartridge, accounting for at least 65% of the cost. Reusing empty factory ammunition cases can greatly reduce the cost per shot since cases can be reused several times before they wear out.
However, a fired case requires that several operations be performed to restore it to a condition suitable for firing. A reloader has control over these processes, but also must be careful to ensure that the resulting cartridge has the proper dimensions to fit the firearm's chamber.
A measurement that is of particular concern is the cartridge's headspace dimension or measurement. Headspace is defined as the length of a cartridge or case as measured from the rear face, or head, to a point of selected intermediate diameter on the tapered shoulder. Headspace is associated with the linear, or front to rear, play of a cartridge in the chamber when the action is closed. If the headspace is too small, the action will not close. If there is too much headspace, the rear of the cartridge is unsupported. When the case expands upon firing, a too-short case can stretch atypical amounts and even rupture as the case's shoulder is blown forward. If the reloader resizes the case excessively and sets the shoulder back too far, the excess headspace condition is created again. Eventually, the stretched brass will succumb to fatigue and crack and break.
However, even cartridges fired in firearms under the correct headspace conditions undergo dimensional changes that must be corrected during the reloading process. Resizing returns the case to the proper dimensions to ensure reliable functioning and assures the case neck grips the bullet tightly. A reloading press is used to recondition the cartridge case using a reloading die and a shell holder.
Various approaches to measuring cartridge headspace are known. However, every type of cartridge requires the use of a separate measurement gauge because the reference diameter at the shoulder differs among cartridge sizes. Another approach involves the attachment of one of five interchangeable bushings to a pair of calipers in order to measure the length of the case from the case-add to the datum line on the case shoulder. Bushings must be changed depending upon the type of case to be measured.
Therefore, a need exists for a new and improved ammunition measurement tool that allows multiple cartridge sizes to be tested with one tool without removing the tool from the calipers. In this regard, the various embodiments of the present invention substantially fulfill at least some of these needs. In this respect, the ammunition measurement tool according to the present invention substantially departs from the conventional concepts and designs of the prior art, and in doing so provides an apparatus primarily developed for the purpose of multiple cartridge sizes to be tested with one tool without removing the tool from the calipers.